The Universal Mobile Telecommunication System (UMTS) is one of the third generation mobile communication technologies designed to succeed GSM. 3GPP Long Term Evolution (LTE) is a project within the 3rd Generation Partnership Project (3GPP) to improve the UMTS standard to cope with future requirements in terms of improved services such as higher data rates, improved efficiency, and lowered costs. The Universal Terrestrial Radio Access Network (UTRAN) is the radio access network of a UMTS and Evolved UTRAN (E-UTRAN) is the radio access network of an LTE system. In an E-UTRAN, a wireless device such as a user equipment (UE) 150 is wirelessly connected to a radio base station (RBS) 110a commonly referred to as an evolved NodeB (eNodeB), as illustrated in FIG. 1a. Each eNodeB 110a-c serves one or more areas each referred to as cells 120a-c, and are connected to the core network. In LTE, the eNodeBs 110a-c are connected to a Mobility Management Entity (MME) 130 in the core network. A positioning node, also called a location server, in the control plane architecture in FIG. 1a is connected to the MME 130. The positioning node is a physical or logical entity that manages positioning for a so called target device, i.e. a wireless device that is being positioned, and is in the control plane architecture referred to as an Evolved Serving Mobile Location Center (E-SMLC) 140. As illustrated in FIG. 1a, the E-SMLC 140 may be a separate network node, but it may also be a functionality integrated in some other network node. In a user plane architecture, the positioning is a part of a Secure User Plane Location (SUPL) Location Platform (SLP). Hereinafter, the general term wireless device may be a UE, a laptop, a small radio node or base station, a relay, or a sensor. The UE may be a mobile telephone, a pager, a headset, a laptop computer and other mobile terminals. The wireless device may also refer to a device or node being positioned in general, often referred to as a Location Service (LCS) target. LTE Positioning Protocol (LPP) and LTE Positioning Protocol annex (LPPa) are protocols used for carrying out positioning in the control plane architecture in LTE. LPP is also used in the user plane architecture, whilst LPPa may be used to support user plane positioning. There may also be LPP extensions, e.g. LPPe, which may be included in LPP messages. When receiving a positioning request, the E-SMLC may request positioning related parameters from eNodeB via LPPa. The E-SMLC then assembles and sends assistance data and the request for the positioning to the target wireless device, e.g. the UE, via LPP. FIGS. 1b-c illustrate example architectures and protocol solutions of a positioning system in an LTE network. In the control plane solution, illustrated in FIG. 1b, the UE communicates with the E-SMLC transparently via the eNodeB and the MME over LPP, and the eNodeB communicates with the E-SMLC transparently via the MME over LPPa. The user plane solution illustrated in FIG. 1c does not rely on the LPPa protocol, although 3GPP allows for the possibility of inter-working between the control and user plane positioning architectures. The SLP is the positioning node for user-plane positioning, similar to E-SMLC for control plane positioning, and there may or may not be an interface between the two positioning servers.
UE positioning is a process of determining UE coordinates in space. Once the coordinates are available, they may be mapped to a certain place or location. The mapping function and delivery of the location information on request are parts of a location service which is required for basic emergency services. Services that further exploit a location knowledge or that are based on the location knowledge to offer customers some added value are referred to as location-aware and location-based services. The possibility of identifying a wireless device's geographical location in the network has enabled a large variety of commercial and non-commercial services, e.g., navigation assistance, social networking, location-aware advertising, and emergency calls. Different services may have different positioning accuracy requirements imposed by an application. Furthermore, requirements on the positioning accuracy for basic emergency services defined by regulatory bodies exist in some countries. An example of such a regulatory body is the Federal Communications Commission regulating the area of telecommunications in the United States.
In many environments, a wireless device position can be accurately estimated by using positioning methods based on Global Positioning System (GPS). Nowadays, networks also often have a possibility to assist wireless devices in order to improve the device receiver sensitivity and GPS start-up performance, as for example in an Assisted-GPS (A-GPS) positioning method. GPS or A-GPS receivers, however, may not necessarily be available in all wireless devices. Furthermore, GPS is known to often fail in indoor environments and urban canyons. A complementary terrestrial positioning method, called Observed Time Difference of Arrival (OTDOA), has therefore been standardized by 3GPP. In addition to OTDOA, the LTE standard also specifies methods, procedures, and signaling support for Enhanced Cell ID (E-CID) and Assisted-Global Navigation Satellite System (A-GNSS) positioning. In future, Uplink Time Difference of Arrival (UTDOA) may also be standardized for LTE.
E-CID Positioning
With E-CID, the following sources of position information are involved: the Cell Identification (CID) and the corresponding geographical description of the serving cell, the Timing Advance (TA) of the serving cell, the CIDs and the corresponding signal measurements of the cells (up to 32 cells in LTE, including the serving cell), as well as Angle of Arrival (AoA) measurements. The following UE measurements can be utilized for E-CID in LTE: E-UTRA carrier Received Signal Strength Indicator (RSSI), Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), and UE receive-transmit (Rx-Tx) time difference. The E-UTRAN measurements available for E-CID are eNodeB Rx-Tx time difference, TA Type 1 corresponding to (eNodeB Rx-Tx time difference)+(UE Rx-Tx time difference), TA Type 2 corresponding to eNodeB Rx-Tx time difference, and uplink (UL) AoA. UE Rx-Tx measurements are typically used for the serving cell, and e.g. RSRP and RSRQ as well as AoA can be utilized for any cell and can also be conducted on a frequency different from that of the serving cell.
UE E-CID measurements are reported by the UE to the positioning server over the LPP, and the E-UTRAN E-CID measurements are reported by the eNodeB to the positioning node over the LPPa.
OTDOA Positioning
With OTDOA, a wireless device such as a UE measures the timing differences for downlink reference signals received from multiple distinct locations. For each measured neighbor cell, the UE measures Reference Signal Time Difference (RSTD) which is the relative timing difference between a neighbor cell and the reference cell. As illustrated in FIG. 2, the UE position estimate is then found as the intersection 230 of hyperbolas 240 corresponding to the measured RSTDs. At least three measurements from geographically dispersed RBSs 210a-c with a good geometry are needed to solve for two coordinates of the UE. In order to find the position, precise knowledge of transmitter locations and transmit timing offsets is needed. Position calculations may be conducted, for example by a positioning node such as the E-SMLC or the SLP in LTE, or by the UE. The former approach corresponds to the UE-assisted positioning mode, and the latter corresponds to the UE-based positioning mode.
In UTRAN Frequency Division Duplex (FDD), an SFN-SFN type 2 measurement (SFN stands for System Frame Number) performed by the UE is used for the OTDOA positioning method. This measurement is the relative timing difference between cell j and cell i based on the primary Common Pilot Channel (CPICH) from cell j and cell i. The UE reported SFN-SFN type 2 is used by the network to estimate the UE position. The OTDOA and other positioning methods such as E-CID are to be used also for emergency calls. Hence the response time of these measurements should be as low as possible to meet the emergency call requirements.
Positioning Reference Signals
To enable positioning in LTE and facilitate positioning measurements of a proper quality and for a sufficient number of distinct locations, new physical signals dedicated for positioning, such as positioning reference signals, (PRS) have been introduced, and low-interference positioning subframes have been specified in 3GPP. PRS are transmitted from one antenna port according to a pre-defined pattern, as described in more detail below.
A frequency shift, which is a function of a Physical Cell Identity (PCI), can be applied to the specified PRS patterns to generate orthogonal patterns and model the effective frequency reuse of six (R6), which makes it possible to significantly reduce neighbor cell interference on the measured PRS and thus improve positioning measurements. Even though PRS have been specifically designed for positioning measurements and in general are characterized by better signal quality than other reference signals, the standard does not mandate using PRS. Other reference signals, e.g., cell-specific reference signals (CRS) may also be used for positioning measurements.
PRS are transmitted in pre-defined positioning subframes grouped by a number N_prs of consecutive subframes, i.e. one positioning occasion, as illustrated in FIG. 3. Positioning occasions occur periodically with a certain periodicity of N subframes, corresponding to a time interval T_prs between two positioning occasions. The standardized time intervals T_prs are 160, 320, 640, and 1280 ms, and the number of consecutive subframes N_prs are 1, 2, 4, and 6.
General UE Radio Access Capability
The UE radio access capability parameters that are currently specified in the 3GPP technical specification TS 36.306 comprise:                ue-Category, which indicates e.g. the maximum number of supported layers for spatial multiplexing in downlink;        Radio Frequency (RF) parameters, such as supportedBandListEUTRA which defines what E-UTRA RF bands that are supported by the UE. For each band, support for either only half duplex operation, or full duplex operation is indicated. For Time Division Duplex (TDD), the half duplex indication is not applicable;        Measurement parameters, such as interFreqNeedForGaps and interRAT-NeedForGaps. These parameters define for each supported E-UTRA band whether measurement gaps are required to perform measurements on other supported E-UTRA radio frequency bands and on each supported RAT/band combination;        Inter-RAT parameters, which are used e.g. for indication of the supported band lists for UTRA FDD, UTRA TDD, GSM/EDGE Radio Network (GERAN);        General parameters, such as accessStratumRelease which defines the release of the E-UTRA layer 1, 2, and 3 specifications supported by the UE e.g. Rel-8 and Rel-9, and deviceType which defines whether the device does not benefit from NW-based battery consumption optimisation;        Closed Subscriber Group (CSG) Proximity Indication parameters, such as intraFreqProximitylndication, interFreqProximitylndication and utran-ProximityIndication which define whether the UE supports proximity indication in the RAT (E-UTRAN or UTRAN) cells comprised in the UE's CSG whitelist. The indication is thus used to inform whether the UE is able to report that it is entering or leaving the proximity of cell(s) included in its CSG whitelist, wherein the CSG whitelist may either be manually entered via a UE interface or autonomously detected by the UE;        Neighbor cell System Information (SI) acquisition parameters, such as intraFreqSI-AcquisitionForHO, interFreqSI-AcquisitionForHO, utran-SI-AcquisitionForHO which define whether the UE supports acquisition of relevant information from a neighboring intra-frequency cell by reading the SI of the neighboring cell using autonomous gaps, and reporting of the acquired information to the network.        
The currently defined UE radio access capabilities and the lack of associated information available in the network and especially in the positioning node, have an impact on the positioning measurement requirements and on positioning performance, and causes unnecessary operations and procedures performed by the network.